Apparatus for dressing gear teeth grinding wheels



July- 2 1, 1953; c. s. DAVIS, JR., arm. 2,646,0 APPARATUS FOR DRESSING GEAR TEETH GRINDING WHEELS Filed July is, 1950 q A 2 Sheets-Sheet 1 JNVENTORS CHARLES s oAvladn .MJHN 5.31, 5,.m.

ATTDR NEY y 1, 1953 c. s. DAVIS, JR., E1 2,646,030

APPARATUS FOR DRESSING GEAR TEETH GRINDING WHEELS Filed July 19, 1950 3 Sheets-Sheet 2 I INVENTORS. HARLES 5.DAVIE|,..IR. JOHN E. RICE: ..|R.

By/z/m MA/ ATTEIRNEV Patented July 21, 1953 NT QFFICE 7 2,646,030 APPARATUS FOR DRESSING GEAR 'rEs-rn GRINDING WHEELS Charles S. Davis, Jr., New York, N. Y., and John E. Rice, .112, Pompton Mains, N. J'., assignors to Curtiss-Viright Corporation, a corporation of Delaware Application July 19,1950, Serial No.174,742

mass. (01. 125-11) This invention relates to gear ztooth grinding and is particularly directed to a method and apparatus for dressing a gear tooth grinding wheel of a generating-type gear tooth grinding machine. As used herein, the term gear tooth is intended to be broad enough to include not only the usual spur and helical gear teeth but also the teeth of other toothed wheels, the teeth of a rack, the helical teeth of a worm as Well as other helical threads.

A generating type gear tooth grinding machine generally hasa disc'like abrasive grinding Wheel for grinding the teeth of a conventional spur gear and each working face of said abrasive wheel has a profile of a side of a rack tooth adapted to mesh with the teeth of said gear. In the involute gear system a rack tooth has a straight-side profile.

, In order to ease or minimize the shock of,

engagement and disengagement of gear teeth when in operation, it is common practice to modify slightly the profile of; said teeth from their theoretically correct profile," for example, by relieving said profile at the first and/or last points of contactwith the meshing teeth. An object of the present invention comprises the provision of a novel and simple. method of apparatus for dressing the disc-like abrasive wheel of a generating-type grinding machine so that the profile of'each working face of said abrasive wheel is made slightly concave whereby said wheel profile will generate said modified tooth profile.

Other objects of the invention will become apparent'upon 'r'eadingthe annexeddetailed description in connection with the drawing in which:

Figure 1 illustrates an'abrasive wheel for a generating-type gear tooth grinding machine, said wheel being viewed along its axis of rotation;

, Figure 2 is a view of said abrasive wheel taken along line 22 of Figures 1 and 4;

Figure 3 is an enlarged radial sectional view of the peripheral portion of said abrasive wheel;

and r Figure 4 is a diagrammatic View of an apparatus for dressing said abrasive wheel in accordance with the invention.

Referring to the drawing, reference numeral i9. designates'the disc-like abrasive Wheel for a generating-type gear tooth grinding machine. Theabrasive wheel it has a pair of substantially conical working surfaces I2 and I4 coaxial with and disposed adjacent to the periphery of said I 2 wheel, said surfaces converging in a radially out ward direction. In addition, the annular surface 15 at the periphery of the abrasive wheel joining the working surfaces l2 and Hi, generally has a convex circular profile. v v

In a plane including the axis of said disclikeabrasive' wheel, the conical working surfaces 52 and i l of said wheel generally have the' straight-sided profile of the sidesof a rack tooth adapted to mesh with the teeth of the gear to be ground. It has been foundidesirable, however, to make said working surfaces [2 and it slightly concave so as to modify slightly the profile of the gear teeth to be ground from their theoretically correct profile. Thus in Figure 3 the distance M designates the maximum departure of the surfaces l2 and i l from their theoretically correct straight-sidedrack tooth profile and the angle (1 (Figures 2 and 3) is equal to the pressure angle of the teeth to be ground. The use of an abrasive grinding wheel having such concave Working surfaces results in a slight modification of the gear teeth ground thereby which minimizes the shock of engagement and disengagement of said gear teeth during operation of said gear. For purpose of illustration, this slight concavity of the profile of the conical working surfaces [2 and M of the abrasive wheel has been exaggerated in- Figures 2 and 3. In general, the maximum departure M of said working surfaces from the straight-sided profile of a rack tooth is made quite small and generally will be less than In Figures land 4, the circle i5 separates the addendum and the .dedendum portions of the rack tooth profile of the surface i2 and it so surfaces of the abrasive wheel each have a straight-sided rack tooth profile, said working surfaces are dressed by a mechanism having means for reciprocating a pair of dressing tools (one for each surface) along straight line paths over said surfaces. Said dressing tool paths are coplanar and are inclined to each other and to a plane midway between the ends of the abrasive wheel with said mid-plane bisecting the angle between said paths and with the axis of said wheel lying in the plane of said paths. With this prior art arrangement, the plane of said dressing tool paths is radial relative to the axis of said wheel. I

Applicants have found that the desired con-= cavity'of the working. surfaces of the abrasive a wheel can be obtained by modifying the above described prior art arrangement so that the plane of said dressing tool paths is no longer radial relative to the wheel axis and instead said plane intersects the dressing wheel along a chord smaller than the diameter of said wheel, for example along line 2-2 of Figures 1 and 4. When the abrasive wheel is dressed with this offset arrangement, the profile of each conical working surface l2 and Iii of a dressing wheel is slightly concave in a radial plane, as illustrated in Figures 2 and 3, the actual curvature of the profile of said surfaces in a radial plane-being, a hyperbola. The precise nature of this curve: is immaterial however because, as already stated, the magnitude of the departure M of the profile of the working surfaces 52 and Hi from straight lines is small. The magnitude of said departure M can be varied by varying the position of the line 22 so as to vary the distance L (Figures 1 and 4) between said line and a parallel radius of the abrasive wheel. This distance L is termed the dresser offset distance. The offset distance L determines the angle b between the line 22 and a radial line through the point of intersection of the pitch circle i5 and said line 2-2-, said latter angle 12 being termed the dresser offset angle. Obviously when, as in the past, the plane of the dresser tool paths is radial relative to the axis of the abrasive wheel, then the offset angle 1) and the offset distance L are both equal to zero.

Figure 4 illustrates apparatus for adjustably supporting the abrasive wheel dressing mechanism on'the grinding machine so that the mag nitude of the departure M of the concave profile of the abrasive wheel surfaces l2 and it from a straight line can be varied as desired. In Figure 4, reference numeral 2!! designates a portion of a generating type gear tooth grinding machine. The abrasive wheel [0 is mounted on said machine portion for rotation about the axis of a shaft 2! 7 The machine 2!] has a linear guideway 22 along which a bracket 24 is adjustably secured by screws 25. The path of said guideway 22 is parallel to the plane of rotation of the abrasive wheel it} but is offset from the axis of said wheel. The bracket 24 has a pivot pin 26 disposed parallel to the axis of the abrasive wheel l0 and disposed so that said pivot axis moves along a line XX radial relative to the axis of said wheel when the bracket 24 is adjusted along its guideway 22. A second bracket 28 is connected to the pivot pin for pivotal adjustment about the axis of said pin relative to the first bracket 21!.

In 'order that the brackets 24 and 28 can be locked in any one of a plurality of positions of relative adjustment about the axis ofithe pin 26, at least one of said brackets is provided with a circular slot 39 having its center on the axis of the pivot pin 2%. As illustrated, the bracket 24 is provided with a slot 30 and a nut 3|, threaded on a bolt extending through said slot, is adapted to lock the bracket 28 to the bracket as in any one of a plurality of positions about the pivot axis 26. The range of said pivotal adjustment, is limited by the length of the slot 3 3.

A conventional dresser mechanism 32 (Figures 2 and 4) is mounted on a linear guideway 34 on the bracket 28 by screws 36, said guideway 34 permitting adjustment of the mechanism 32 along a direction parallel to line 22 of Figure 42. The mechanism 32 has a pair of rods 38 and 43 extending therefrom at an angle to each other. The rods 38 and 40 are mounted for reciprocation along their respective longitudinal axes. For this purpose, a shaft 42 extends into the housing of the mechanism 32, said shaft being connected to the rods 38 and by a gear and rack construction (not shown), as is conventional, whereby oscillation of the shaft 42 about its axis causes reciprocation of the rods 38 and 58 along their respective axes. A gear M on the shaft 62 meshes with a worm shaft 36, this latter shaft projecting from the housing for operation by the operator. With this arrangement oscillation of the worm shaft 46 causes reciprocation of the rods 38' and 323. Preferably the rods 38 and it move in opposite directions such that when one is being extended the other is being retracted.

As illustrated in Figure 2, arms es and it are secured to the rods 38 and 4:) respectively and each arm t8 and '58 has a head 52 carrying a diamond dresser tool 5-45. The rods 38 and it and their respective arms is and 59 are disposed so that the cutting ends on the two diamond dressers 54 move along straight line paths which are inclined to each other and are coplanar with the plane of Figure 2. Thus as viewed in Figures 1 and 4 the cutting ends on the diamond dressers move in the plane defined by the section line 2--2 while in Figure 2 the cutting end of each dia- I mond dresser 54 moves along its respective linear angle.

path '15-")? across its working face E2 or it of the abrasive wheel. The mid-plane of the abrasive wheel bisects the angle between the two straight line diamond dresser paths Y Y. The angle 0 (Figure 2) between each of said paths and the plane of said wheel is termed the diamond setting As stated in Patent No. 2,022,061, in a conventional dresser mechanism 32 each diamond setting angle 0 is adjustable. Accordingly no description of a specific means for adjusting this angle 0 is deemed necessary herein.

When the dresser offset angle 1) is zero, as in prior practice, the diamond setting angle 0 obviously is made equal to the pressure angle a of the gear teeth to be ground.

In using the apparatus so far described, the

P bracket 2 is first adjusted along the guideway 22 to a position such that the axis of the pin an intersects the pitch circle [5 of the abrasive wheel 10. In addition the angles 12 and c of the apparatus must be properly set. These angles will depend on the pressure angle a of the teeth of From these two equations the angles 17 and 0 can be determined and the apparatus set accordingly.

For use in said equations, the working length or height H of the profile of each gear tooth can be determined by actual measurement or from the following equation:

tan b 1rgS tan a H 360 where g is the angle in degrees through which the gear rotates while any one tooth of said gear is in meshing engagement, S is the diameter of the base circle of said gear, and a is the pressure angle of the gear teeth to be ground.

of the teeth of the gear to be ground are'symmetrical, then the two diamond setting angles are made equal. When however each said gear tooth is non-symmetrical in that they have differentpressure angles a, then the two diamond setting angles will not be the same and each said diamond setting angle will depend on the magnitude of thepressure angle of the side of the gear tooth its respective abrasive wheel surface II or M is to grind.' s

In the position illustrated in the drawing, the bracket 23 is pivotally adjusted to one end of the slot 30 so that the offset angle b is a maximum, and with the proportions illustrated, said maximum angle is approximately 60 degrees. When the bracket 28 is pivotally adjusted to the other end of the slot 30, said ofiset angle b is a minimum as permitted by the slot an and, with the proportions illustrated, the minimum offset angle is approximately 40 degrees. Obviously the range of adjustment of the offset angle b can be varied by changing the length of the are I subtended by the slot 3!} about the axis of the pin 26. Thus the arcuate length. of the slot 30 could be increased to 90 degrees to permit adjustment of the offset angle 12 between zero and 90 degrees. With such an arrangement the dressing mechanism could be used with a zero offset angle, as in the prior art, or with any desired offset angle up to the maximum offset angle of 90 degrees. It has been found however that the magnitude of the departure M is negligible for offset angles less than 40 degrees.

Preferably the periphery 16 of the abrasive wheel I0 is dressed by the dresser mechanism at the same time the working surfaces i2 and M of said wheel are dressed. For this purpose, the

shaft 42 is provided with a bevel gear 6i meshing with a bevel gear 62 on a shaft 84, thereby connecting the shaft 64 to the operating shaft 46 for joint oscillation. Ihe shaft 1 has an offset arm 65 which carries a diamond dresser tool 63 so that saidtool is adapted to oscillate over the peripheral surface it of the abrasive wheel upon oscillation of the shaft 64 by the shaft 46. The diamond dresser 68 engages the periphery it of the abrasive wheel approximately on the radial line XX of said wheel so that the axis Z- z of the shaft 6 3 intersects said radial line a small distance radially inwardly of; said periphery approximately equal to the desired radius of the ally adjusted about the axis of the pin 2e to the limit position illustrated, the axis Z-'-Z makes a small angled with the radial line X-X, said angle being equal approximately to one-half the range of pivotal adjustment of the bracket 28 as limited by theslot 30. the axis ZZ, the magnitude of the angle 01 is sufiiciently'small inall positions of adjustmentof the bracket 28 that the radius dresser 63 Will dress the periphery it of the abrasive wheel to an arcuate profile which is a sufficiently close approximation of the desired circular profile.

Withthis disposition of When, as is generallythe case, the two sides I detailin its present preferred embodiment, it

will be obvious to those skilled in the art, after understanding our invention, that various changes and modificationsmay be made therein without departing from the spirit or scope there the axis of said wheel; adjustable means locking said brackets together in any one of a. plurality of positions of relative pivotal adjustment about saidaxis; support means having a linear guideway; means supporting one of said brackets on said guide'way in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing too-l drive mechanism. mounted on the other of said brackets, said mechanism including a pair of inclined shafts. to be reciprocated thereby; and a pair of abrasive wheeldressing tools, one for and secured to each of said shafts for reciprocation of each tool by its shaft along a straightline path inclined to a plane perpendicular to the axis of said wheel and inclined to the corresponding path of the other tool. a

2. Apparatus for dressing a disc-like abrasiv wheel having a pair of annular substantially conical surfaces adjacent to its periphery; said apparatus comprising first and second brackets pivotally connected on an axis disposed parallel to the axis of said wheel; adjustable means lock.- ing said brackets together in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having a linear guideway; means supporting one of said brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing tool drive mechanism mounted on the other of said brackets, said mechanism including a pair of inclined shafts to be recip-rocated thereby; and

a pair of abrasive wheel dressing tools, one for each of said surfaces, said tools bein connected to saidshafts' for reciprocationthereby along straight-line paths with each said path being inclined to the other path and to a plane perpenv brackets pivotally connected about an axis disposed parallel to the axis of said wheel; adjustable means locking said brackets together in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having alinearguideway; means supporting-one of said brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket th-erealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing tool drive mechanism mounted on the cther of said "brackets, said mechanism including a pair of inclined shafts to be reciprocated thereby; and a pair of abrasive wheel dressing tools, one for each of said surfaces, each of said tools being connected to one of said shafts for reciprocation thereby along a straight-line path over its respective wheel surface, said straight-line dressing tool paths belng coplanar and inclined to each other with the angle between said paths being bisected by a plane disposed midway between the end faces of said wheel and disposed perpendicular to both the axis of said Wheel and to. the plane of said paths.

4. Apparatus for dressing a disc-like abraswe wheel having a pair of annular substantially conical surfaces adjacent to its periphery and having a convex surface at its periphery connecting said side surfaces with the profile of said side surfaces substantially corresponding to the profile of the sides of a rack tooth; aid apparatus comprising first and second brackets pivotally connected on an axis disposed parallel to the axis of said wheel; adjustable means locking said brackets together in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having a linear g u1deway; means supporting one of said brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing tool drive mechanism mounted on the other of said brackets, said mechanism including a pair of inclined shafts to be reciprocated thereby and including a third shaft for osci1lat1on thereby; a pair of abrasive wheel dressing tools, one for each of said conical wheel surfaces, each of saro tools being connected to one of said pair of shafts for reciprocation thereby along a straight-line path over its respective wheel surface; straightline dressing tool paths being coplanar andunclined to each other and to a plane perpendicular to the wheel axis withsaid latter plane and the plane of said paths being perpendicular; anda third dressing tool for and engageable with said convex wheel surface adjacent to the intersection of radial line with said convex surface, said third dressing tool being connected to said third shaft for oscillation thereby about an axis intersecting said radial line radially inwardly 'of the periphery of said wheel.

5-. Apparatus for dressing a disc-like abrasive wheel having a. pair of annular substantially conical converging side surfaces adjacent to its periphery and having a substantially circular convex surface at its periphery connect ng said side surfaces with the profile of said side surfaces substantially corresponding to the profile of the sides of a rack tooth; said apparatus comprising first and second brackets pivotally conheatedon an axis disposed parallel to the axis of said wheel; adjustable means locking said brackets together in any one of a plurality of positions of relative pivotal ad ustment about said axis; means limiting the range of pivotal adjustment of said brackets; support means havinc: a linear guideway; means supporting one of brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one-bracket therealong said pivot axis moves along a line radial relative to the ax1s of said wheel; dressing tool drive mechanism mounted on. the other of said brackets, said mechanism including a pair of inclined shafts to be reciprocated thereby and including a third shaft for oscillation thereby; a pair of abrasive wheel ressing tools, one for each of said conical wheel surfaces, each of said tools being connected to one of said pair of shafts for reciprocation thereby over its respective wheel surface along a straight-line path, said straight line dressing tool paths being coplanar and inclined to each other and to a plane perpendicular to the wheel axis; and a third dressing tool for and engageable with said convex wheel surface adjacent to the intersection of said radial line with said convex surface, said third dressing tool being connected to said third shaft for oscillation thereby about an axis intersecting said radial line inwardly of the periphery of said wheel a distance approximately equal to the radius of said convex surface and the axis of said oscil lation being so oriented that when said other bracket is substantially at its mid-position of pivotal adjustment said axis of oscillation is perpendi ular to said radial line.

6. Apparatus for dressing a. disc-like abrasive wheel having an annular substantially conica surface adjacent to its periphery, the profile of said surface substantially corresponding to the profile of a side of a rack tooth; said abrasive wheel dressing apparatus comprisin first and second brackets pivotally connected together an axis disposed parallel to the axis of said wheel; adjustable means locking said brackets together in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having a linear guideway; means supporting one of said brackets on said gu Zeway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of'said wheel; dressing tool drive mechanism mounted on the other of said brackets at a point more removed from said wheel than said pivot axis, said mechanism includin a shaft and means connected to said shaft for reciprocating said shaft along its axis; and a dressing tool carrier secured to said shaft for reciprocating a dressing tool over said surface along a straight line path parallel to the axis of said shaft with said one bracket being positioned along said. linear uideway so that said pivot axis adjacent to the wheel periphery.

7. Apparatus for dressing a disc-like abrasive wheel having an annular substantially conical surface adjacent to its periphery, the profile of said surface substantially corresponding to the profile of a side of a rack tooth; said abrasive wheel dressing apparatus comprisin first and second brackets pivotally connected together on an axis disposed parallel to the axis of said wheel; adjustable means locking said brackets to ether in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having a linear guideway; means supporting one of said brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing tool drive mechanism mounted on the other of said brackets at a point more removed from said wheel than said pivot axis, said mechanism including a shaft and means connected to said shaft for reciprocating said shaft along its axis; and an abrasive wheel dressing tool secured to said shaft for reciprocation thereby over said'surface along a straight line pathparallel to the axis of said shaft and coplanar with a chord of said wheel smaller than the diameter of said wheel with said one bracket being positioned along said linear guideway so that said pivot axis intersects said wheel adjacent to the wheel periphery.

8. Apparatus for dressing a disc-like abrasive wheel having a pair of annular substantially conical surfaces adjacent to its periphery; said apparatus comprising first and second brackets pivotally connected on an axis disposed parallel to the axis of said wheel; adjustable means looking said brackets together in any one of a plurality of positions of relative pivotal adjustment about said axis; support means having a linear guideway; means supporting one of said brackets on said guideway in any one of a plurality of positions therealong, said guideway being disposed so that upon movement of said one bracket therealong said pivot axis moves along a line radial relative to the axis of said wheel; dressing tool drive mechanism mounted on the other of said brackets, said mechanism including a pair of shaftsto be reciprocated thereby with the axis of each shaft being inclined to the axis of the other shaft and to a plane perpendicular to the axis of said wheel; and a pair of abrasive wheel dressing tools, one for each of said surfaces, each of said tools being connected .to one of said shafts for reciprocation thereby over its associated surface along a straight-line path parallel to the axis of its associated shaft.

CHARLES S. DAVIS, JR. JOHN E. RICE, JR.

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